Liquid crystal display devices, having features such as lightness in weight, slimness and low power consumption, have been used as display devices for GA devices such as personal computers, televisions, mobile terminals, car navigation devices, game consoles, and the like.
As one of methods of manufacturing liquid crystal display panels, one drop filling (ODE) method has been put into practical use. In the ODE method, a liquid crystal display panel is manufactured by forming a frame-shaped sealing member on a substrate, dropping a liquid crystal material onto an area surrounded by the sealing member, overlaying another substrate on the substrate under vacuum, and releasing the substrates under atmospheric pressure to pressurize the paired substrates with atmospheric pressure. The liquid crystal material to be used in the ODE method is degassed to remove unnecessary components such as air and moisture premixed in the liquid crystal material.
In addition, if impurities are mixed in the liquid crystal material, the liquid crystal material needs to be purified to a high degree since the impurities may cause display failure of the liquid crystal display panel. In the conventional purification of the liquid crystal material, general purification of organic compounds such as recrystallization, distillation, liquid chromatography or the like alone is performed and removal of water-soluble impurities is insufficient. Since the water-soluble impurities contained in the liquid crystal material causes display unevenness on the liquid crystal display panel, technology of removing the water-soluble impurities has been proposed (cf. Patent Literature 1 and Patent Literature 2). The display unevenness on the liquid crystal display panel, caused by the water-soluble impurities contained in the liquid crystal material, is particularly remarkable on the liquid crystal display panel of active matrix driving system.